Apparatus for the preparation of metal powder



June 18, 1957 E. A. LEZBERG ETAL 2,795,819

APPARATUS FOR THE PREPARATION OF METAL POWDER Filed Aug. 25, 1954 '1 w62 v V l 32 g 3/ F /6. 2 k I I 53 5/ 5 0 ll 7 40 0 as O 7 4/ I I 44 J n137 Q: f 19 58 3e 1 34 INVENTORS ERWIN A. LEZBERG ALBERT M. LORDAPPARATUS FOR THE PREPARATION OF METAL POWDER Erwin A. Lezherg,Lakewood, and Albert M. Lord, Olmsted Falls, Ohio, assignors to theUnited States of America as represented by the Secretary of the NavyApplication August 23, 1954, Serial No. 451,724 9 Claims. (Cl. Ill-2.4)(Granted under Title 35, U. S. Code (1952), see. 266) This inventionrelates to the preparation and collection of oxide free metal powder, ofextremely small particle size.

There are several methods in use for production of fine metal powders,such as atomization of molten metal in heated gas jets, the formation ofan electric arc in a liquid between the metal in Wire form and anadjoining electrode, mechanical disintegration by means of ball, rolleror hammer mills or attrition, condensation of metal vapor, orelectrolytic reduction. However, it has been found that metal particlesderived from the prior methods fail to meet requirements as to extremefineness and freedom from oxidation so that the required product isunobtainable from known commercial sources.

The primary object of the invention, therefore, is to provide a sourceof metal particles which are free of oxidation. Another object is toprovide a method of producing metal particles of the described typewhich is simple in operation. Still another object is to provide amethod for fine metal powder production which is subject to easy controlof the particle size. Other objects and features of the invention willappear on consideration of the following description of the method andapparatus used, as illustrated in the accompanying drawings, in which:

Fig. l is a schematic view of the apparatus employed in the method; and

Fig. 2 is a detail of the structure of Fig. 1 taken along lines 2-2 ofFig. 1.

Generally stated, the method found to meet the stated requirementsinvolves fusion of the metal in wire form by an electric arc in an inertatmosphere with appropriate conveyance of the condensed metal dropletsto a receptacle.

In Fig. l, the apparatus may be examined in three major units, the wirefeed equipment 10, the electric arc unit 11 and the receptacle 12. Thewire feed equipment is adapted bodily from the electric welding art andcomprises a feed mechanism 15, driven by motors 16 and 17, passing wire18 through guide tube 19 to the arc unit 11, all under control of thecontrol unit 20. This feed equipment is arranged to feed the wire, whichmay be magnesium, aluminum or any desired metal substance, into an openelectric arc at a constant arc voltage, automatic controls maintainingadequate electrode spacing for this purpose after initial electrodecontact. Such equipment is currently manufactured and sold in the openmarket. (For example, products of The Auto Arc-Weld Manufacturing Co.,Cleveland, Ohio, and Patent 2,516,777.)

The electric arc unit 11 includes a vertically positioned tube 30serving as a gas chamber for inert gas flow and as a support for the arcelectrodes. The upper tube end is closed by a cap 31 in the end of whichis attached a sight tube 32 terminating in a glass window 33 throughwhich the arc terminals in tube 30 may be visually examined.

The base of tube 30 is closed by a cap 34 which at its lower endconverges into the exit pipe connection 35. A cooling chamber is formedabout tube 30 by the shell 36 inlet duct 37 connecting at the base ofthe shell and cited States Patent Patented June 18, 1957 outlet duct 38connecting at the top thereof. Valve 39 in inlet 37 permits control ofthe coolant flow.

The two are electrode holders are horizontally disposed about midway inthe tube 30 and shell 36. The wire electrode holder 40 is a tube withone end attached to, and having egress into, tube 30. At the other endof the holder tube 40 is attached to a three way T coupling 41, theoutlet of which in line with tube 4% being connected to, and supportingwithin tube 40, a refractor tube 42 of crystallized alumina, such asAlundum. Tube 42 projects at its outer end 43 a short distance beyondcoupling 41 and at its inner end 44 a short distance into tube 30, andserves as a guide and holding sleeve for the wire 18 when threadedtherethrough. The space between tubes 40 and 42 at the inner endsthereof is open to permit free passage of gas to the arc space.

The opposed electrode holder 50 is also a tube transversely penetratingthe walls of tubes 30 and 36 at points in axial alignment with tube 40,with the inner end flush with the wall of tube 40 and the outer endextending a short distance beyond the Wall of shell 36. The outer end oftube 50 terminates in a bushing 51 forming an attachment means for thefixed electrode rod 52 to which the electrode 53, enclosed by tube 50,is attached. This electrode, which is preferably made of graphite, hasan enlarged cylindrical head 53 extending about midway into thearcchamber. The outer end of the electrode rod 52 is secured to theterminal block 54 of cable 55 through which direct current electricpower is obtained; and the corresponding power terminal block 56 for thewire is attached to the feed nozzle 57 of the wire feed unit 10, thecable 58 connecting the block to the power source.

To prevent oxidation of the are fused metal, inert gas, such as helium,argon and the like, is forced into the arc chamber of tube 30. From anypressurized source this gas is led by conduit 61, one end of conduit 61connecting to the transverse outlet of T coupling 41 and the other endconnecting directly to the sight tube 32 at the top of the arc chamber.Gas inflow at the sight tube insures clarity of view of the electrodesduring the fusion step, the particle mist being swept downwardly by thegas movement. A pressure gauge 62 is connected to conduit 61 and athermoelectric thermometer 63, including gauge 64 and thermocouple 65,gives arc chamber temperatures. Valve 66 in conduit 60 controls the gasflow.

The receptacle 12 for the metal particles is a flat based cup 70 with atransverse edge flange 71, to which a fiat cover plate 72 is attached,as by bolts 73. About middepth in the cup, a perforated plate 74 of anyinert material such as metal or plastic is secured, the function of thisplate being to distribute the gas bubbles and scrub the metal particlesfrom the gas stream. A central inlet pipe 75 passing through the coverplate 72 and perforated plate 74, is suspended by a union 76 from theend of arc chamber pipe 35 so that its lower end is above the flatbottom of the receptacle. An exit pipe 77, for the inert gas is attachedto the closure plate 72. Normally the receptacle contains an inertliquid 78 such as kerosene, to a depth covering the perforated plate 74.

In operating the apparatus the coolant valve 39 and helium gas valve 66are opened to insure in the arc chamber an air free atmosphere and asafe maintained temperature. Gas entering the T 41 moves along theannular space between the tubes 40 and 42 so that it sweeps the regionof the arc. Gas entering by way of the sight tube 32 clears the upperchamber space for are inspection through window 33. Power switches arethen closed to supply electric current to the wire feed unit 10 and tothe arc circuit terminals 54 and 56. The wire, which is assumed to bemagnesium, is thus fed through amperes being suitable for aone-sixteenth inch diameter wire in a helium atmosphere. These dropletsare condensed in the helium gas as a spray and swept toward the exitpipe 35, the receptacle pipe 75 and the receptacle liquid, the metalparticles being wetted by the liquid and forming a suspension therein tobe removed as desired. The gas, after discharging some additionalparticles by scrubbing action in the perforated plate 74, passes outthrough exit pipe '77.

It is noted that the fineness of the particles produced can becontrolled by the current density of the arc. Below a given value forthe metal mere fusion occurs, while above this value small particlesdevelop as a fine spray. The feed rate is fixed by the arc voltage andmay be adjusted as desired. Also, the arc length may be varied bysetting the arc control, according to known methods. The particlesproduced are extremely fine, sizes ranging from one to five microns, andspherical in shape. Due to the immediate solidification of the particlesthere is no tendency to agglomeration and being free of oxidation, theparticles are at once usable.

Modified procedures and equipment may also be employed, other thanherein above described. For example, instead of the liquid bubbling ofthe particle laden gas use might be made of liquid scrubbing,electrostatic, centrifugal or canvas bag screening methods. Also, whilemagnesium is referred to as the metal, and helium the gas, any stablemetal or inert gas may be used, the procedure involving a physicalbreakdown of the metal under certain conditions of electric arc densitywithin an inert atmosphere to prevent oxidation. It is understoodtherefore that the invention may be practiced otherwise than asspecifically described, within the scope of the appended claims.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed is:

1. Apparatus for producing metal particles of extreme fineness from wireof said metal, comprising an arc chamber, a source of electric current,a fixed electrode in said chamber, a wire in said chamber, electricallyconducting means between said source and said wire and electrode, meansfor advancing said wire into are forming relationship with saidelectrode, a receptacle for liquid and for particles derived from theformed arc, said liquid being inert to said particles, and means forpassing said particles from said arc into said liquid without oxidationthereof, said particle passing means including a tube connecting saidelectrode and receptacle for passing pressurized inert gas from saidelectrode through said liquid.

2. Apparatus for producing metal particles as defined in claim 1 andmeans for channeling said gas at multiple points of flow through saidliquid.

3. Apparatus for producing metal particles of extreme finenesscomprising an electric arc chamber, a fixed electrode in said chamber, awire mounted for movement into said chamber in arcing relationship tosaid electrode, a source of electric power for supplying arc current tosaid wire and electrode, a particle receptacle containing an inertliquid, a conduit extending from said are chamber to a point displacedfrom the bottom of said receptacle, and means for forcing particlesformed in the wire-electrode arcthrough said conduit and into saidliquid without oxidation of said particles, whereby the particles arecollected in said receptacle.

4. The apparatus for producing metal particles of ex treme fineness asdefined in claim 3, said particle forcing means including a gasconnector tube between said chamber and receptacle, and additional meanssupported in said receptacle for. dispersing the gas throughout thevolume of said liquid.

'5. Apparatus for producing metal particles of extreme finenesscomprising an electric arc chamber, an electrode in said chamber, meansfor feeding a wire into are producing relationship with said electrode,a source of electric current for are formation between said wire andelectrode, a receptacle for said metal particles, a conduit connectingsaid arc chamber and receptacle, means for forcing metal particlesformed at said are into said receptacle, and means for holding said arechamber at an approximately constant temperature.

6. A method of producing metal particles of extreme fineness whichcomprises forming an electric are between the metal in wire form and afixed inert electrode, enveloping said are in an inert gas, producing acurrent density at the arc of such value as to obtain disintegration ofthe wire in particle form, advancing said wire continuously while thewire is being disintegarated in said arc, and conveying all of said gas,laden With metal particles, through a liquid bath wherein the particlesare suspended.

7. The method of producing metal particles as defined in claim 6 withtheadditional step of dispersing the gas flow in its movement throughsaid bath.

8. The method of producing fine metal particles, which comprises formingan electric are between the metal in wire form and an inert electrode,enveloping said are in an inert gas, producing a current flow throughsaid are of such value as to disintegrate the metal to fine particles,conveying said particles and all of said gas to a liquid receptacle, andwetting said particles in said liquid.

. 9. The method of producing fine metal particles as defined in claim 8,said current having a value of around 260 amperes for one-sixteenth inchdiameter magnesium wire in a helium atmosphere.

References Cited in the file of this patent UNITED STATES PATENTS2,189,387 Wissler Feb. 6, 1940

1. APPARATUS FOR PRODUCING METAL PARTICLES OF EXTREME FINENESS FROM WIREOF SAID METAL, COMPRISING AN ARC CHAMBER, A SOURCE OF ELECTRIC CURRENT,A FIXED ELECTRODE SAID CHAMBER, WIRE IN SAID CHAMBER, ELECTRICALLYCONUCTING MEANS BETWEEN SAID SOURCE AND SAID WIRE AND ELECTRODE, MEANSFOR ADVANCING SAID WIRE INTO ARCH FORMING RELATIONSHIP WITH SAIDELECTRODE, A RECEPTACLE FOR LIQUID AND FOR PARTICLES DERIVED FROM THEFORMED ARC, SAID LIQUID